Super-Altro 16: A Front-End System on Chip for DSP Based Readout of Gaseous Detectors

This paper presents the architecture, design and test results of an ASIC specifically designed for the readout of gaseous detectors. The primary application is the readout of the Linear Collider Time Projection Chamber. The small area available (4 mm² /channel) requires an innovative design, where sensitive analog components and massive digital functionalities are integrated on the same chip. Moreover, shut down (power pulsing) features are necessary in order to reduce the power consumption. The Super-Altro is a 16-channel demonstrator ASIC involving analog and digital signal processing. Each channel contains a low noise Pre-Amplifier and Shaping Amplifier (PASA), a pipeline ADC, and a Digital Signal Processor (DSP). The PASA is programmable in terms of gain and shaping time and can operate with both positive and negative polarities of input charge. The 10-bit ADC samples the output of the PASA at a frequency up to 40 MHz before providing the digitized signal to the DSP which performs baseline subtraction, signal conditioning, drift correction and zero suppression. The chip has been fabricated in a 130 nm CMOS technology. Test measurements show correct functionality of the full system, and demonstrate that, using appropriate design techniques, the extensive digital circuitries produce little or no degradation of analog performance (particularly noise).